1. Field of the Invention
The present invention relates to a method, system, and program for initiating and using information used for host, control unit, and logical device connections.
2. Description of the Related Art
In certain computing environments, multiple host systems may communicate with one or more control units, such as an IBM Enterprise Storage Server (ESS)®, for data in a storage device managed by the ESS receiving the request. The control unit manages access to storage devices, such as interconnected hard disk drives through one or more logical paths. (IBM and ESS are registered trademarks of IBM). The interconnected drives may be configured as a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. The control unit may configure logical volumes that define regions of storage space in the storage devices the control unit manages.
The control unit or an adaptor in the control unit may maintain volume group information, where each volume group associates one or more logical volumes with either one or more hosts, or one or more host ports. The volume group information may comprise a bitmap, where there is a bitmap value for each logical volume available through the control unit indicating whether the logical volume is available for a particular host and port connection. In current systems, the control unit may initialize bitmaps for every possible host and port connection to indicate the accessibility of all logical volumes to that host and port connection. The number of bitmaps that may be allocated comprises the number of host ports times the number of control unit ports through which the hosts connect times the number of bits needed to represent all logical volumes, e.g., LUNs, available through the control unit. As the number of logical volumes, ports, and supported host connections on a control unit increases, the amount of memory needed to be allocated for the volume group information increases substantially.
Further, the control unit or adaptor may maintain for each logical volume, e.g., Logical Unit Number (LUN), persistent reservation information. The persistent reservation information is information for a host port, control unit port, and logical volume that is used to manage which hosts are allowed to join or modify the reservation. On a control unit that supports a large number of logical volumes that are accessible through Input/Output (I/O) ports on the control unit, the potential number of relationships requiring persistent reservation information is the number of ports times the number of logical volumes times the number of host ports. Each persistent reservation data entry may require from 20 to 256 bytes. In current systems, the control unit reserves space for each possible entry of persistent reservation information. The control unit may also reserve space in memory. As the number of supported logical volumes, host ports, an control unit ports increases, the amount of memory required to be reserved for persistent reservation information increases substantially.